Conventionally, gold (Au), silver (Ag), platinum (Pt), palladium (Pd), rhodium (Rh), iridium (Ir), ruthenium (Ru), osmium (Os), etc. are known as precious metal materials, and are used in various fields, such as decorative members, dental members, electronic members, etc.
However, where these precious metal materials are used in such fields, they are not necessarily satisfactory in mechanical properties, such as hardness, Young's modulus, etc., and durability properties, such as corrosion resistance etc. Besides, there is another problem in that their operability is poor.
On the other hand, in recent years, white gold (Ni—Cu—Au alloy) has attracted attention in the field of ornamental articles, but its hardness has not yet been satisfactory. In addition, the alloy has a poor color tone, and an unsatisfactory corrosion resistance, thereby hardly maintaining aesthetic value. For this reason, the alloy is commercialized by using a plating treatment etc. under the present circumstances. Furthermore, the alloy cannot help having its hardness lowered by a heat treatment, such as brazing etc. Besides, its operability is also poor.